Neuropathology is a discipline that has broad applications across clinical and research fields involving the central and peripheral nervous systems and skeletal muscle. As a clinical service, neuropathology defines diseases of the nervous system by their structural features through the macroscopic, microscopic and, occasionally, ultrastructural examination of biopsy and autopsy material. Much of the research in neuropathology is centred on the study of human disease and observations that generate hypotheses to be tested by experiments in animal models or in tissue culture. Conversely, results from experimental studies aid the interpretation of pathological features of human disease.
Scientific and clinical advances in the last ten years affecting Neuropathology have been driven by the introduction of new techniques and concepts and by the need to communicate more effectively with those involved in the direct clinical care of patients and with patients and relatives themselves. A spirit of communication and collaboration has strengthened over the last decade through regular Multidisciplinary Team Meetings and collaborative research projects.
Many developments have occurred in the last ten years across the whole spectrum of adult, paediatric and forensic neuropathology. However, in this article, we focus upon some of the changes that have evolved in tumour pathology, an area of primary responsibility for most practicing neuropathologists, and in muscle pathology. We go on to describe progress in the post-mortem diagnosis and in the understanding of neurodegenerative diseases.
Advances in tumour pathology
Neuropathology is often at the centre of the clinical decision making process. The pathological diagnosis of tumours in patients is crucial for their management and treatment. Major changes in clinical practice in relation to tumours of the nervous system have come with the introduction of molecular diagnostics. Molecular evaluation of tumours is now routine (Table 1), but diagnosis remains dependent primarily on the microscopic appearances of a tumour in routine sections stained with haematoxylin and eosin.
Figure 1: INI-1 immunohistochemistry of an atypical
/rhaboid tumour (main image, no staining within tumour cells but vascular endothelial cells show nuclear brown staining). By comparison, a primitive neurectodermal tumour (PNET), inset, shows strong nuclear staining of tumour cells. Scale bar = 100µm.
Scientific discoveries that hold most promise for a change in clinical practice in relation to tumours of the nervous system have been due to the application of array-based and deep sequencing technologies and by the use of mouse models as a foundation for in vivo therapeutic testing. During the last decade, application of immunocytochemistry (Figure 1) has greatly improved the classification of brain tumours. In addition, neuropathology plays a key role in establishing the primary diagnosis for tumour tissue used in array-based techniques and fluorescence in situ hybridization (FISH) for the molecular classification of glioblastoma [1], astrocytoma [2], oligodendroglioma [3] and medulloblastoma [4]. Such work has had a direct effect on the management and treatment of brain tumours.
Advances in muscle pathology
The characterisation of new forms of inherited muscle disease has grown exponentially over the last ten years. New proteins whose mutations cause certain phenotypes are described several times a year. Basic histological and histochemical evaluation of frozen muscle specimens remains as an important investigation for categorising muscle pathology [5]. More in-depth analysis of biopsies, including genetic testing, is often carried out at NCG (National Commissioning Group) centres. This illustrates one way in which super-specialist high-cost services and professional working practices can be developed and flourish. Data on muscle pathology, biochemistry and genetics are produced at such a rapid rate that published papers and books have difficulty in keeping pace, so many websites (e.g. www.neuromuscular.wustl.edu/) are now the main sources of up-to-date information.
Post-mortem diagnosis and understanding neurodegenerative diseases
Developments in neuropathology in the last decade have played a significant role in the continuing search for the effective diagnosis and treatment of neurodegenerative diseases. An appreciation of neuropathological changes and mechanisms of disease are essential for the interpretation of neuroimaging and of biomarkers in the blood and CSF used in the diagnosis of patients with dementia [6]. Relating the changes in the human brain to those in transgenic mouse models has allowed significant progress in our understanding of disease processes during the last 10 years.
Figure 2: Lewy neurites and Lewy bodies in the substantia nigra of an 82 year-old male with Dementia with Lewy Bodies. Main image – α-synuclein immunohistochemistry showing fine wire-like Lewy neurites (arrows to two) and Lewy bodies (arrow-head to one), scale bar = 100µm. Inset: H&E appearance of a single nigral neuron with some remaining melanin pigment, but also a single Lewy body with a dense core and paler periphery (arrowhead). Scale bar = 20µm.
Recognition of genetic abnormalities in familial diseases has had a profound effect on neuropathology and vice-versa. For example, the known genetic causes of Parkinson’s disease include mutations in the α-synuclein gene reported in the late 1990s [7]. The presence of this synapse-related protein, as insoluble accumulations in Lewy bodies and in neurites (Figure 2) in sporadic Parkinson’s disease, has stimulated physiological experiments to determine the effects of excessive synuclein on synaptic function. Using transgenic mice that over-express α-synuclein, whole cell patch clamp recordings have shown that high levels of expression of α- synuclein alter synaptic function and suggest that synaptic dysfunction may occur early in Parkinson’s [8].
Figure 3: A confocal image of a mouse cerebral artery in transverse section showing how tracers such as dextran (green) can be co-localised with laminin (red) in the artery wall. Co-localisation of dextran and laminin is seen as dark blue. By such use of confocal microscopy it was shown that interstitial fluid and solutes drain from the brain along perivascular basement membranes. Scale bar = 10µm.
Reproduced with permission from reference 9.
Technological advances have also increased our understanding of CNS disease. Confocal microscopy, together with continuing advances in immunocytochemistry, have allowed proteins, tracers and ligands to be co-localised with a degree of accuracy that was previously unknown [9] (Figure 3). This has greatly enhanced our capacity to investigate the functional aspects of tissues and cells in the normal and diseased nervous system.
Alzheimer’s disease
Alzheimer’s disease remains the most common form of dementia world-wide. With an ageing population, it is estimated that there are 700,000 people with dementia in the UK, most of whom will suffer from Alzheimer’s disease. Extracellular plaques of insoluble amyloid-β (Aβ) and intracellular, intraneuronal, neurofibrillary tangles containing tau protein have long been recognised pathological features of Alzheimer’s disease. During the last 10 years, there have been very significant advances in our understanding of the disease; too many to mention here. As an example, however, attention has focussed on the failure of elimination of Aβ from the elderly brain and how such a failure may be responsible for dementia. Age brings loss of enzymes that degrade Aβ in brain tissue [10] , reduced absorption of Aβ into the blood [11] and impaired elimination of Aβ along perivascular drainage pathways [12]. As the level of soluble Aβ in the brain appears to correlate with cognitive decline in Alzheimer’s disease [13], toxicity of soluble Aβ has also become a focus of research [14].
Immunotherapy whereby plaques of insoluble Aβ are removed from the brains of patients with Alzheimer’s disease has been introduced [15]. Neuropathological studies of post-mortem brains from treated patients have revealed mechanisms by which Aβ is removed from plaques by microglia and how such removal reduces the accumulation of tau in neurites [16]. These observations supply key data for the future development of immunotherapy.
Other studies, using transgenic mice, have shown that tau spreads from neuron to neuron [17] whereas Aβ diffuses through the extracellular spaces and drains along perivascular pathways by which fluid and solutes drain from the brain to regional lymph nodes [9,18].
Other neurodegenerative diseases
Animal models of prion diseases have been used to distinguish between the toxic and infective roles of prion proteins and this could lead to the development of therapies for Creuzfeldt-Jacob disease (CJD) [19]. Just before the present decade began, the UK was in a public health dilemma with the advent of variant CJD contracted by ingestion of meat from cows infected with bovine spongiform encephalopathy (BSE). In the last ten years there has been intense surveillance by neuropathologists to identify any new cases of vCJD as they occur. Biochemical analyses have shown that the prion protein in variant Creutzfeldt-Jakob disease is remarkably stereotyped, in contrast to the considerable hetero- geneity that exists in sporadic CJD [20).
Figure 4: P62 immunohistochemistry labels a neuronal intranuclear inclusion within a cortical neuron in an uncommon neurodegenerative disease associated with dementia. Scale bar = 10µm.
The last decade has seen significant advances in our understanding of frontotemporal lobar degeneration (FTLD) [21,22] associated with dementia in a slightly younger age group than Alzheimer’s disease. Several new types of FTLD have been identified through a combination of gene studies and the neuropathological characterisation of intracellular protein inclusions. One of the more common forms of this disease was previously recognised as a form of motor neuron disease (FTLD-MnD). Particularly significant has been the identification of new pathological proteins in most tau-negative forms of FTLD. P62 is a protein within the ubiquitin functional pathway and immunohistochemistry for p62 has superseded ubiquitin as a diagnostic tool for intracellular inclusions (Figure 4) in FTLD [21].
The role of neuropathology in Brain Tissue Banks
Although there was much public concern in the UK at the beginning of the decade about retention of brains at post mortem, there have been significant developments in brain and tissue banking during the past ten years. The formation of the Human Tissue Authority and associated Act is an example of this. Brain-banking entails cooperation of patients, carers and relatives, together with the organisational skills and funding from charities and the Medical Research Council (e.g. www.brainsfordementiaresearch .org.uk). Neuropathologists play a key role in brain and tissue banks, not only in the acquisition and storage of the material but also in its accurate diagnosis and documentation [23]. This is an essential service that ensures that researchers who use material from brain banks are supplied with firm and accurate diagnostic neuropathological data.
References
1. Kurian K. Recent advances in Glial Tumours. ACNR 2009:8;24-6.
2. Phillips HS, Kharbanda S, Chen R, et al. Molecular subclasses of high-grade glioma predict prognosis, delineate a pattern of disease progression, and resemble stages in neurogenesis. Cancer Cell 2006:9;157-73.
3. Scheie D, Andresen PA, Cvancarova M, et al. Fluorescence in situ hybridization (FISH) on touch preparations: a reliable method for detecting loss of heterozygosity at 1p and 19q in oligodendroglial tumors. Am J Surg Pathol 2006:30;828-37.
4. Lu Y, Ryan SL, Elliott DJ, et al. Amplification and overexpression of Hsa-miR-30b, Hsa-miR- 30d and KHDRBS3 at 8q24.22-q24.23 in medulloblastoma. PLoS One 2009:4;e6159.
5. Sewry CA, Jimmenez-Mallebrera C, Brown SC, et al. Diseases of muscle. In: Love S, Louis DN, Ellison DW, editors. Greenfield’s Neuropathology. Eighth ed. London: Hodder Arnold; 2008:1725-820.
6. Jack CRJ, Knopman DS, Jagust WJ, et al. Hypothetical model of dynamic biomarkers of the Alzheimer’s pathological cascade. Lancet Neurol 2010:9;119-28.
7. Polymeropoulos MH, Lavedan C, Leroy E, et al. Mutation in the alpha-synuclein gene identified in families with Parkinson’s disease. Science 1997:276;2045-7.
8. Wu N, Joshi PR, Cepeda C, et al. Alpha-synuclein overexpression in mice alters synaptic communication in the corticostriatal pathway. J Neurosci Res 2009:Dec 22. [Epub ahead of print].
9. Carare RO, Bernardes-Silva M, Newman TA, et al. Solutes, but not cells, drain from the brain parenchyma along basement membranes of capillaries and arteries. Significance for cerebral amyloid angiopathy and neuroimmunology. Neuropathol Appl Neurobiol 2008:34;131-44.
10. Love S, Miners S, Palmer J, et al. Insights into the pathogenesis and pathogenicity of cerebral amyloid angiopathy. Front Biosci 2009:14;4778-92.
11. Bell RD, Zlokovic BV. Neurovascular mechanisms and blood-brain barrier disorder in Alzheimer’s disease. Acta Neuropathol 2009:118;103-13.
12. Weller RO, Preston SD, Subash M, et al. Cerebral amyloid angiopathy in the aetiology and immunotherapy of Alzheimer disease. Alzheimers Res Ther 2009:Oct 12;1(2):6. [Epub ahead of print].
13. McLean CA, Cherny RA, Fraser FW, et al. Soluble pool of Abeta amyloid as a determinant of severity of neurodegeneration in Alzheimer’s disease. Ann Neurol 1999:46;860-6.
14. Walsh DM, Selkoe DJ. Abeta Oligomers – a decade of discovery. J Neurochem 2007:101;1172-84.
15. Holmes C, Boche D, Wilkinson D, et al. Long-term effects of Abeta42 immunisation in Alzheimer’s disease: follow-up of a randomised, placebo-controlled phase I trial. Lancet 2008:372;216-23.
16. Nicoll JA, Wilkinson D, Holmes C, et al. Neuropathology of human Alzheimer disease after immunization with amyloid-beta peptide: a case report. Nat Med 2003:9;448-52.
17. Clavaguera F, Bolmont T, Crowther RA, et al. Transmission and spreading of tauopathy in transgenic mouse brain. Nat Cell Biol 2009:11;909-13.
18. Weller RO, Djuanda E, Yow HY, et al. Lymphatic drainage of the brain and the pathophysiology of neurological disease. Acta Neuropathol 2009:117;1-14.
19. Mallucci GR. Prion neurodegeneration: starts and stops at the synapse. Prion 2009:3;195-201.
20. Head MW, Bunn TJ, Bishop MT, et al. Prion protein heterogeneity in sporadic but not variant Creutzfeldt-Jakob disease: UK cases 1991-2002. Ann Neurol 2004:55;851-9.
21. Cairns NJ, Bigio EH, Mackenzie IR, et al. Neuropathologic diagnostic and nosologic criteria for frontotemporal lobar degeneration: consensus of the Consortium for Frontotemporal Lobar Degeneration. Acta Neuropathol 2007:114;5-22.
22. Pickering-Brown SM. Recent progress in Frontotemporal lobar degeneration. Neuropathol Appl Neurobiol 2010:36;4-16.
23. Alafuzoff I, Arzberger T, Al-Sarraj S, et al. Staging of neurofibrillary pathology in Alzheimer’s disease: a study of the BrainNet Europe Consortium. Brain Pathol 2008:18;484-96.
